Weak cerebral dominance has been proposed as an important factor in reading disability. From existing evidence, it appears that information, through reading, is processed by the dominant side of the brain, that is, mostly by the left side of the brain in right-handed people and mostly by the right side of the brain in left-handed people. Many individuals with reading disabilities are left-handed. Estimates are that as many as 70% of left-handed individuals have some degrees of reading disability. This has been taken by some investigators as an indication of possible mixed dominance in brain function.
It has been suggested that individuals without a clearly dominant brain hemisphere have what may be termed cross-talk between the two hemispheres which may interfere with the efficient processing of reading material. It is thus important to be able to diagnose and treat reading disabilities that involve the improper directing of visual information to the hemispheres of the brain.
It is well established that retinal processing of visual information is almost entirely lateralized. The left half of the retinal field from the left eye and the left half of the retinal field from the right eye project to the left brain. The right half of the retinal field from the right eye and the right half of the retinal field from the left eye project to the right brain. Researchers have attempted to restrict initial input of visual information to either the right or left brain by way of glasses having lenses that are opaque in a vertical portion. While it is recognized that information crossover can occur between the hemispheres, restricting initial input to one side can cause more orderly processing of information in individuals who do not have clear lateralization of function. Unfortunately, as a subject moves his eyes, without simultaneously turning his head, the opaque portions of the glasses lenses move with respect to the subject's visual field, allowing some visual input to reach the supposedly blocked portion of the retina.
A known lens that will remain stationary with respect to the eye as the eye moves is a contact lens. Tinting of contact lenses, both for cosmetic purposes or for lessening light input to sensitive eyes is also known, although no occlusion takes place, merely lowering of the light intensity. Of course, these lenses do not completely block visual input on any part of the lens, and could not be used to selectively block input to vertical hemispheres.
Contact lenses that have automatic orientation means are known in the art as well, for example see U.S. Pat. No. 3,431,327 and U.S. Pat. No. 3,279,878. The '327 patent discloses a bifocal contact lens that is formed with a small metal weight near one edge. The weight causes the contact lens to rotate on the wearer's eye until the weight is at its lowest point, putting the horizontally-split visual field in proper perspective. The '878 patent discloses a lens that is thicker at one peripheral portion. The lens again rotates until the heavy thicker portion is at its lowest position, with the horizontally-split field properly aligned.